Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based or thermal, have at least one printhead from which droplets of ink are directed towards a recording sheet. Within the printhead, the ink is contained in a plurality of channels. Power pulses cause the droplets of ink to be expelled as required from orifices or nozzles at the end of the channels. Continuous ink stream printers are also known.
In a thermal ink-jet printer, the power pulses are usually produced by resistors, each located in a respective one of the channels, which are individually addressable to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in that particular channel and ink bulges from the channel orifice. At that stage, the bubble begins to collapse. The ink within the channel retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel orifice and towards the recording medium whereupon hitting the recording medium a spot is formed. The channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink. Operation of a thermal ink-jet printer is described in, for example, U.S. Pat. No. 4,849,774.
The ink-jet printhead may be incorporated into either a carriage-type printer or a page-width type printer. The carriage-type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles), at a time, on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. The procedure is repeated until the entire page is printed. In contrast, the page-width printer includes a stationary printhead having a length equal to or greater than the width or length of a sheet of recording medium. The paper is continually moved past the page-width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page-width ink-jet printer is described, for instance, in U.S. Pat. No. 5,192,959.
It has been recognized that there is a need to maintain the ink ejecting nozzles of liquid ink printheads, such as an ink-jet printhead, by periodically cleaning the orifices when the printhead is in use by purging or vacuum withdrawal of ink and/or by capping the printhead when the printer is out of use or is idle for extended periods. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime or to purge the printhead nozzles before use and occasionally during use to ensure that the printhead channels are completely filled with ink, contain no contaminants or air bubbles, and do not dry out from not being used. Typically, the ink-jet printhead is moved into position or vice versa with a maintenance and/or priming station for printheads of ink-jet printers. In a page-width printhead, the maintenance of the nozzles throughout the entire length of the printhead is especially critical since not all of the individual jets may be fired during the printing of a single sheet of paper or over many sheets of paper.
On occasion, ink can collect on the transport belt during purging of the printhead nozzles, during routine maintenance of the printhead, or during printing itself if a paper jam occurs and ink is deposited onto the transport belt instead of onto the recording medium. Consequently, while a liquid ink printer is designed to effectively control any undesirable depositing of ink on the transport belt, such situation do arise. Consequently, it is desirable to clean the transport belt of ink and/or other contaminants before printing is resumed, since ink deposited on the belt can ruin an otherwise perfectly printed recording medium.
Various cleaning mechanisms for cleaning belts and other devices present in printing machines are illustrated and described in the following disclosures which may be relevant to certain aspects of the present invention.
In U.S. Pat. No. 3,867,170 to Ferguson et al., a method for cleaning liquid developers from the imaging surface of an electrostatographic imaging system is described. The imaging surface is cleaned with a cleaning liquid which is miscible with the liquid developer. A cleaning web absorbs the cleaning liquid and contacts the imaging surface to dilute and dissolve the liquid developer.
U.S. Pat. No. 4,568,174, to Strange, describes a photoreceptor descumming device for cleaning contaminants from a photoreceptor surface. The device includes a flexible web moving into engagement with the photoreceptor surface.